Anthony Gardner, the US ambassador to the European Union, has told a Dublin audience of business people that Brexit will "complicate" efforts for transatlantic co-operation on a wide range of issues.

Mr Gardner was addressing the independence day lunch of the American Chamber of Commerce, in Dublin’s Doubletree hotel. He said the US-EU relationship requires an “EU that is cohesive, effective and outward looking”.

He said greater cooperation between Europe and the US was needed on issues such as data transfer laws, sanctions on nations such as Russia, and energy policy.

“The departure of the U.K. will complicate some of those issues,” he said.

Mr Gardner likened the current domestic politics of the UK to the Netflix series, the House of Cards.

In reference to the upcoming US presidential election, he joked the US is about to provide the world with “three months of free entertainment”.

He said Europe and the US are “sailing into choppy waters” and were encountering “demagogues”.

“We need some US optimism in Brussels,” he said.